The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Hybrid electric vehicles (HEV) can selectively use different energy sources for propulsion as needed in order to achieve optimal fuel efficiency. An HEV can selectively use either or both of an internal combustion engine and a torque machine(s) connected to an energy storage device (ESD). If the torque machine is a motor/generator unit (MGU), a high-voltage battery module is used as the ESD for propulsion and operational control.
One HEV includes a hybrid powertrain including an engine stop/start system wherein the engine automatically shuts down during ongoing vehicle operation (autostop) and automatically restarts (autostart) using the torque machine(s). The hybrid powertrain system preferably includes a regenerative braking system for recharging the ESD via the torque machine(s) and the ability to selectively shut down the engine during vehicle idle, referred to as an autostop event.
The high-voltage MGU can be used as a belt-alternator-starter (BAS) system in lieu of an alternator. The BAS applies torque to a serpentine belt of the engine when a driver signals an intention to resume travel after an autostop event. Torque from the torque machine can spin the engine for a short duration to crank the engine until it fires and runs. During starting of the engine in response to the operator initiating a key-on state, a crankshaft-mounted auxiliary or 12-volt starter motor can provide cranking torque to crank and start the engine.
A BAS HEV uses a high-voltage battery or energy storage device (ESD) supplying high-voltage electrical power to a voltage inverter within the electrical system of the HEV. After an autostop event, the torque from the torque machine to spin the engine during the engine restart can cause accessory speed to flair. Accessory speed flair occurs when the accessories are spun at a greater rotational speed than expected or intended to be operated at due to an unrestricted torque from the torque machine when attempting to restart the engine. Additionally, during an autostop event, the accessories may not be turned when the engine is shut off, losing feature functionality, e.g., an air conditioner compressor is shut off thereby losing cabin cooling when the engine is off.